1038 THE NERVOUS SYSTEM 



fibres of the white rami from the lower thoracic nerves are in greater part directed 

 downward in the sympathetic trunk, and also downward in its peripheral 

 branches, to be distributed to the abdominal viscera. In all cases, however, some 

 of the fibres of the thoracic white rami terminate in the ganglia nearest their 

 junction with the trunk, while others pass into the nearest peripheral branches. 

 In this way the white rami from all the thoracic spinal nerves, especially those 

 of the mid-region, are directly concerned in the innervation of the thoracic 

 viscera, lungs, oesophagus, aorta, etc. 



The first thoracic ganglion is larger than the other ganglia of this region and is 

 irregular in form. It may be narrowly ovoid or semilunar. It lies in front of the 

 neck of the first rib, behind the pleura, and on the medial side of the costo- 

 cervical trunk (superior intercostal artery), which vessel separates it from the 

 prolongation of the portion of the first thoracic nerve which passes to the brachial 

 plexus. It sometimes fuses with the inferior cervical ganglion, and, on the other 

 hand, sometimes extends to the upper part of the second rib to fuse with the 

 second thoracic ganglion. The result of the latter fusion resembles the stellate 

 ganglion of the carnivora, and when it occurs, is sometimes referred to as the 

 ganglion stellatum. When well developed, the first ganglion sends a branch to the 

 cardiac plexus, forming the fourth cardiac nerve of Valentin. 



The second thoracic ganglion, triangular in shape and almost as large as the 

 preceding, is sometimes placed on the costo-vertebral articulation, and is some- 

 times partly concealed by the first rib. 



The third to the ninth thoracic ganglia are usually placed opposite the heads of 

 the corresponding ribs, but the tenth and eleventh may lie on the bodies of the 

 vertebrse. 



The fibres passing from the ganglia form two groups of branches, the central 

 and the peripheral. 



The central branches are the grey rami communicantes, which pass from the 

 ganglia to the corresponding spinal nerves. After they have joined with the 

 anterior primary divisions of the nerves, the fibres of these rami divide into four 

 groups: — (1) Fibres which pass medial ward along the roots of the nerves to supply 

 vessels of the membranes of the spinal cord, or enter a meningeal or recurrent 

 branch for the same pm-pose; (2) fibres which enter the spinal ganglion and 

 terminate there (sensory sympathetic fibres); (3) fibres which pass dorsalward 

 into the posterior primary divisions of the nerves; (4) fibres which pass lateral- 

 ward in the anterior primary divisions of the nerves. The last two groups of 

 fibres are distributed to the muscle of the blood-vessels of the body-walls, to the 

 skin-glands, and to the muscles of the hairs of the body. 



The peripheral branches of the ganglia form two series, an upper and a 

 lower. 



Those of the upper series pass from the upper four or five ganglia ventralward 

 to be distributed as follows: — 



(1) Pulmonary branches which accompany the intercostal arteries toward their aortic 

 origin without forming plexuses around them, and pass to the posterior puhnonary plexus 

 (fig. 789). 



(2) Aortic branches, some of which arise directly from the gangha and some from the 

 pulmonary branches, and unite with branches from the cardiac plexus and from the splanchnic 

 nerves to surround the aorta as the thoracic aortic plexus (fig. 789). This plexus accompanies 

 the aorta into the abdomen and there joins with the ca-liac (solar) plexus. 



(.3) (Esophageal branches join with the crsophageal plexus of the vagus. 



(4) Vertebral branches, some of which pass with the nutrient arteries into the bodies of 

 the vertebra) and some of which pass to the median line and there anastomose with similar 

 branches from the opposite side (commissural branches). 



The peripheral ganglionic branches forming the lower series consist largely of 

 efferent and afferent fibres from the spinal nerves, which pass through the ganglia 

 and reinforce the sympathetic filaments proper. Thus composed, these branches 

 run ventralward and medialward on the sides of the bodies of the vertebrae and 

 unite to form the splanchnic nerves which supply the abdominal organs, the 

 afferent fibres sei^ving to collect sensory impulses in this domain of the sym- 

 pathetic. 



(1) The great splanchnic nerve may be formed by branches from all the thoracic ganglia 

 from the fifth to the tt^iith inclusive, or it may receive fibres from only two or three of these 



